1. Field of the invention
The present invention relates to a premixing burner for producing hot gas in accordance with the preamble of claim 1. It also relates to a method of operating such a premixing burner.
2. Discussion of Background
A burner has become known from EP-A1-0,210,462 which is formed from at least two double cambered, hollow partial conical bodies, each charged by a tangential air inlet. In the direction of flow, these bodies develop away from one another along diagonals opening in the manner of conical rays. In this process, one cambered body forms an inner cone with a conical opening increasing in the direction of outward flow, while the other cambered body forms an outer cone with a conical opening decreasing in the direction of outward flow. At their ends, the inner cones carry on their entire axial extent one fuel pipeline each for feeding the gaseous fuel, which flows through a plurality of fuel nozzles into the interior of the burner, in order to mix there with the tangentially inflowing combustion air. Moreover, the burner has a separate feed of a liquid fuel, so that we are dealing here with a dual burner. Injection of the liquid fuel is directed axially onto the outer cones in such a way that, depending upon the intensity of the injection, a fuel film of different length and consistency forms there. Apart from the natural evaporation of the liquid fuel due to the radiant heat prevailing there, a significant mixing of fuel comes about due to the tangentially led up combustion air, which due to its swirling motion in the axial direction rolls up the fuel film in layers, so that the production of a strong vortex mixing becomes superfluous. Due to the fact that the impulse of the injection of the liquid fuel is matched to the machine load, the mixture is never too lean or too fat. It is thus possible to achieve the following immediately:
The advantages of a burner with a premixing section, namely little NO.sub.x and CO, arise, so that we are dealing here with a premixing burner.
Good flame stability is guaranteed in a wide operating range, so that it is possible to abandon measures against a flame kickback in the interior of the burner. Moreover, the design configuration of this burner produces an eddying flow which, on the one hand, is low in angular momentum in the center but, on the other hand, has an excess of axial velocity. Because the swirl coefficient increases strongly in the axial direction and reaches the breakdown value at the end of the burner, this produces a vortex return flow which is positionally stable.